The present invention relates to a dielectric ceramic powder composition for forming multilayer ceramic devices having thin dielectric layers with low porosity, and, more particularly, to a densified dielectric composition having a low dissipation factor which meets or exceeds X7R specifications and consists essentially of an admixture of a major component ceramic powder particle and minor component additives the amounts of which are controlled within certain predetermined ratios.
Multilayer ceramic (MLC) capacitors are the most widely used form of ceramic capacitors because of their high volumetric efficiency and their small size. A need exists for a dielectric composition useful in fabricating MLC capacitors with thin layers, e.g., 15 microns or less meeting the EIA, i.e., Electronic Industries Association's specification for X7R-type service. Among the properties which X7R-type dielectric materials must possess are a low dissipation factor (df) of 2.5% or less, an insulation resistance (IR) of at least 1000 ohm-Farads at 25.degree. C. and at least 100 ohm-Farads at 125.degree. C. with no more than .+-.15% deviation in the dielectric constant, i.e., a temperature coefficient of capacitance (TCC) that is less than .+-.15% deviation over the temperature range of -55.degree. C. to +125.degree. C. In addition, the dielectric composition should possess a high dielectric constant (K) of 3500 or above, and must sinter to essentially full density giving a mechanically strong body with good insulation resistance, thermal shock resistance and humidity resistance, e.g., low porosity.
Dielectric materials for X7R-type service find extensive use in electronic equipment for data processing, military applications, automotive applications, telecommunications and other applications in which the material is subjected to substantial changes in temperature, frequency and voltages.
The incorporation of certain additives into formulations based on barium titanate to control certain properties important in the performance of a capacitor is known in the art. Japanese 61-99210, for example, describes a dielectric ceramic based on barium titanate containing oxide(s) of praseodymium, neodymium, samarium, dysprosium, niobium and/or magnesium and the molar ratio of niobium oxide to magnesium oxide is 1:04-1:2.2.
It has been discovered in the present invention, that reduction in the df can be achieved by controlling a predetermined ratio of minor component additives, i.e., dopants or metal oxides in atom %. The composition of the present invention is used to fabricate MLC capacitors with low porosity having thin dielectric layers, e.g., 15 microns or less with a df of 2.5% or less, while retaining other properties of the X7R specifications.